The present invention generally relates to pumping fluid. More specifically, the invention relates to withdrawing and transferring vapor in a sealed manner.
Gasoline vapor is toxic and harmful to the environment. Traditional nozzles on gasoline pumps release harmful quantities such vapor into the atmosphere when such a nozzle is dispensing gasoline a fuel tank, such as that of an automobile. Many gasoline retailers take no steps to prevent this harmful release of fumes.
Adequate reduction or prevention of gasoline vapor release can be achieved by drawing off vapor adjacent to the dispensing of the liquid gasoline. A vacuum line can be attached to the nozzle structure so that a vacuum inlet is positioned adjacent to the end of the nozzle which dispenses the liquid gasoline.
An automobile gasoline tank generally has a tube extending to an opening which is fitted with a cap. A gasoline nozzle is inserted into this tube for dispensing gasoline into the tank. The gasoline vapor released from the liquid gasoline collects primarily within this tube. Therefore, simultaneous withdrawal of vapor from this proximity effectively recaptures the vapor before it is released into the atmosphere.
The withdrawn vapor is transferred to a processing device or back into the original storage tank where it condenses back into liquid gasoline. This essentially recycles the gasoline that otherwise would have harmed the environment. Therefore, a system for withdrawing and transferring the vapor must be sealed so that the vapor is not released into the atmosphere.
As gasoline is dispensed, vapor in the automobile tank is displaced from the tank in the same volume as the liquid flowing in. Similarly, the storage tank from which the gasoline is being dispensed should receive vapor at the same rate, in order to remain at the same pressure. If a greater volume of vapor were transferred to the storage tank than the volume of liquid removed, pressure would build up in the storage tank and eventually release into the atmosphere.
Desirably, vapor is withdrawn proximal to the nozzle at the same volumetric rate that the liquid gas is being dispensed. That vapor is transferred back to the storage tank. Such a vapor withdrawal rate insures that toxic vapor is sufficiently withdrawn at the nozzle. Also, such a vapor withdrawal rate insures that the pressure in the storage tank remains constant.
In a vapor recovery system for a gasoline pump, the vapor pump desirably runs only intermittently-when gasoline is being dispensed. During periods of nonuse, it is desirable to prevent vapor from freely flowing toward the nozzle.
Pumping vapor by means of fans or vaned devices is known. For example, propellers are sometimes used for moving vapor, as on an airplane or a table fan. A propeller can be ducted for pumping vapor through a tube. However, a propeller pump can leak vapor between its blades, especially at low velocities. Furthermore, a ducted propeller allows free flow between its blades when stationary. This makes such a pump impractical for pumping precise quantities of vapor. It is also impractical for pumping in a leak-free application.
A vane pump generally provides a means for pumping vapor in a more precise manner than a propeller type pump. A vane pump has a plurality of flat vanes rotating in a chamber. Between adjacent vanes, a discrete pocket of vapor is moved from an inlet to an outlet within the chamber. The vanes are slidably mounted in a rotor which is offset within the chamber so that the volume of the pocket expands as it moves past the inlet, and contracts as it passes the outlet.
A vane pump thereby provides a system for drawing in and pumping out controlled volumes of vapor. However, a traditional vane pump is impractical for pumping gasoline vapor. Gasoline vapor leaves a residue on pump components which can cause vanes in a traditional pump to stick. Furthermore, a traditional vane pump can leak vapor around a shaft on which the rotor is mounted.
Blockage downstream from a pump causes high fluid pressure to build up between the pump and the blockage. Similarly, an upstream blockage can cause a vacuum buildup. Such pressure can damage components. It is necessary to prevent pressure or vacuum buildup when such a blockage occurs. A common safety system simply vents the pumped vapor from the system through a valve. However, when the vapor is toxic, such a release is undesirable.
Therefore, a need exists for a safety device on a vapor pump that is activatible upon an upstream or downstream blockage that does not vent fluid into the atmosphere.
Furthermore, a need exists for a vane pump that can reliably be used for pumping gasoline vapor.
A need also exists for withdrawing vapor proximal to a nozzle outlet and pumping that vapor in a sealed manner. A need also exists for a vapor recovery system capable of withdrawing and transferring vapor a precise volumetric rate.
Therefore, a further need exists for a vapor pump that does not allow vapor flow through the pump when it is not operating.